Author Topic: NES running on sd2snes  (Read 5509 times)

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Offline antonioks

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NES running on sd2snes
« on: August 08, 2018, 06:29 PM »
Hi everyone, I was seeing and everdrive n64, it has a nes emulator, it would be possible, this emulator to run on sd2snes, and who knows some other console like gb, gbc, game gear through emulation? 8)
Everdrives I own: Mega Everdrive v1, SD2SNES rev. (E1b), Everdrive N64 v2.5

Offline Jdurg

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Re: NES running on sd2snes
« Reply #1 on: August 08, 2018, 07:33 PM »
Not sure if that is even feasible.  The SNES runs off a 3.58 MHz CPU and has 128 kb of RAM.  It's actually not a powerful system at all.  It's the expansion chips in the carts that gives it the power it has.  To run those carts, the FPGA on the SD2SNES needs to be able to simulate the accessory chips.  To run NES software, or GB, or GBC, or Game Gear, etc. would require the simulation of every single chip contained within those consoles, then rewriting the code so that the right data would be sent out from the SD2SNES so you could see the results on your TV.

The Everdrive64 for the N64 has some very rudimentary NES support in there, but not exactly full 100% compatibility.  That's only since the N64 is a far more powerful system than the NES is.

Is it impossible to emulate NES stuff on the SNES via SD2SNES?  I'm not a programmer so I can't say with certainty whether it is or not.  However, unlike the special chips like FX and SA-1, getting other systems to run on the SD2SNES would require more chips to be simulated by the FPGA and that may not be likely.

Offline wprpalmeida

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Re: NES running on sd2snes
« Reply #2 on: August 10, 2018, 05:25 PM »
No

Offline mrpopsicleman

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Re: NES running on sd2snes
« Reply #3 on: August 11, 2018, 08:25 AM »
Short answer? No.

Long answer?
Quote from: ikari_01
well uh
yes and no
it might be possible to get something working but there's no straightforward way to get the picture into the SNES at sufficient speed
I can feed audio directly, but not video
now PPU2 has a secret mode where you can feed it 15 bit digital video
but of course it would be impractical to cut up the snes
lol

OTOH Super Gameboy might not be too far out of reach
as it already works in "real life" through the cartridge bus.

Offline ShyBry

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Re: NES running on sd2snes
« Reply #4 on: August 15, 2018, 06:21 AM »
What if all of a NES game's CHR ROM was pre-loaded into SNES video RAM on startup... Would there be enough bandwidth on the cartridge bus to send button presses, tile indexes, background scroll position, sprite positions, and palette changes?

Would absolutely not work in all cases; some NES ROMs have more CHR ROM than the SNES has video RAM, and many NES ROMs have CHR RAM. Plus this all assumes that a 2A03, a stripped-down 2C02 that outputs tile indexes instead of composite video, and relevant cartridge mapper hardware would all fit on the SD2SNES FPGA. I'm guessing the 2A03 is simpler than the SA-1 but I've no idea about the rest of it.

Might have read a similar idea on the Nesdev forums in a thread about trying to use the 65816's 6502 compatibility mode to run NES games, I can't remember.

Offline Jdurg

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Re: NES running on sd2snes
« Reply #5 on: August 15, 2018, 06:45 AM »
With the video RAM in the SNES totally 64 kilobytes of space, a great number of games would be unable to fit in there as they are larger than 64 kilobytes in size.  Games like the Castlevania series, The Super Mario Brothers series, and Zelda 2 all have more than 64 kb of CHR ROM and therefore would not fit within the video RAM of the SNES.

Also, some NES games used funky techniques to mix in CHR ROM into the PRG ROM in some cases.  So that method of pre-loading the data into the SNES Video RAM just wouldn't be possible i don't think.